PC-relative Branch Range
Conditional branches use the B-type immediate, a signed PC-relative offset in 2-byte units, giving an approximate reach of +/-4 KiB from the current PC.
RISC-V Unprivileged ISA, RV32I control transfer instructionsBEQ
RISC-V BEQ Instruction Details
Instruction ManualB-typeBranch to PC-relative offset if rs1 equals rs2
Instruction Syntax
beq rs1, rs2, offset
Operand Breakdown
Source rs1: first comparison operand.
Source rs2: second comparison operand.
Immediate offset: 13-bit signed branch offset (bit 0 is implicitly 0, ±4 KiB range).
RV32IControl TransferBranch
Related Search Terms
Instruction Encoding
31..25
imm[12|10:5]
24..20
rs2
19..15
rs1
14..12
funct3
11..7
imm[4:1|11]
6..0
opcode
BEQ uses opcode 1100011 (0x63), funct3 000. The rs1 and rs2 fields hold the comparison operands, and the 13-bit immediate encodes the branch offset (±4 KiB).
Format: B-type
opcode: 1100011 (0x63)
funct3: 000 (0x0)
Instruction Behavior
BEQ (B-type, opcode=1100011, funct3=000) compares rs1 and rs2 and takes the branch (to PC + sign-extended 12-bit B-immediate in multiples of 2) if they are equal. The conditional branch range is ±4 KiB. If the condition is false, execution falls through.
Quick Understanding & Search Notes
BEQ is a conditional branch: when rs1 and rs2 satisfy the equal condition, the PC branches to the current PC plus the B-type offset; otherwise execution falls through.
The B-type branch offset is encoded in 2-byte units and reaches about +/-4 KiB from the current PC.
RISC-V conditional branches do not write rd and do not save a return address.
Official Spec Notes
These notes are checked against the RISC-V Unprivileged ISA manual and summarize operation semantics, immediate ranges, and edge behavior.
No Link Register Write
Conditional branches only update the PC based on the comparison result. They do not write rd or save a return address; use JAL/JALR forms for calls and returns.
RISC-V Unprivileged ISA, RV32I control transfer instructionsCommon Usage Scenarios
Comparison & Detection
Understand this scenario with real code like «beq x1, x2, 0x100 # if x1 == x2, branch to pc+0x100».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is B-type.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
Range is ±4 KiB; use jump if beyond
B-type targets are encoded in 2-byte units; without compressed-instruction support, taken targets must be 4-byte aligned
FAQ
What is the BEQ branch range?
Conditional branches use a B-type immediate, giving an approximate reach of +/-4 KiB from the current PC.
What is the difference between signed and unsigned branches?
BLT/BGE compare as signed integers; BLTU/BGEU compare as unsigned integers. BEQ/BNE only test equality of the bit patterns.